The challenge of noise mitigation

December 28, 2018

[1]All photos courtesy McIntosh Perry

by Ibrahim El-Hajj, M.Sc., Arch., EQI, CACB, MRAIC, BCQ, OAA

Many questions can arise when considering the issue of noise mitigation. For example, why might designing to the minimum Ontario Building Code (OBC) requirements not get you a pass when it comes to sound transmission class (STC) rating? Is this a design issue or a blind spot in OBC? Is the tendency to design more compact and smaller units the reason behind noise complaints? Should specification of acoustical performance be considered? While this article is tailored to the requirements of the Ontario Building Code (OBC), a future piece will consider acoustics in the context of the National Building Code of Canada (NBC).

Traditionally, sound control has had limited importance in building design and construction. Nowadays, it is incorporated at various construction stages (from below grade to the building envelope to separation between suites/rooms and operating systems). It has been used:

at below-grade portions of buildings adjacent to subway stations or other sources of vibration;

within mechanical and electrical equipment as well as operating units and devices;

at curtain walls, window walls, spandrel panels, and other cladding systems, as well as at other junctions and construction joints between fire- or acoustically rated assemblies; and

when a building is located in close proximity to highways, subways, rail stations, streetcars, stadiums, airports, aircraft corridors, and similar.

Basically, the discomfort of noise and vibration is caused by three main factors: occupants, building utilities (i.e. system operation), and external sources.

When wondering about the purpose of acoustics and the main sources of noise, it would be prudent to reflect on factors that play into noise control, such as:

human beings and their behaviour, lifestyle, and level of comfort;

the perception of sound versus noise (i.e. noise can be defined as unwanted sound);

side effects and symptoms;

people’s sensitivity, age, and tendency to complain or not complain;

type of noise and vibrations;

density and congestion;

dimensions and volume of the interior space;

layout of suites and building configuration;

acoustical shop drawings;

acoustical specification;

prime consultant co-ordination;

geographical location as well as relevant environmental considerations; and

bylaws, regulations, and the current building code requirements.

Objective of the code

OBC sets minimum requirements for various building components, such as structural systems, fire safety systems, the building envelope, plumbing, and HVAC systems, as well as the elements addressing acoustics.

When it comes to acoustics, requirements are summarized in Parts 3, 5, and 9 of the Ontario Building Code (OBC), addressing the following:

sound control;

protection from noise;

sound transmission;

STC;

STC rating (airborne sound);

determination of STC rating;

the required sound control locations (airborne sound); and

minimum STC rating (airborne).

It is important to note while sound control may be considered as mitigation at the source, protection from noise has to do with path and destination. Reducing, masking, blocking, and soundproofing are all measures with an impact on sound transmission. In this example, OBC considers the dwelling unit or suite in the hotel a potential source of noise.

To learn more, one can refer to OBC’s Article 3.3.4.6, “Sound Transmission,” Article 9.11.1.1, “Determination of Sound Transmission Class Ratings,” Article 9.11.2.1., “Minimum Sound Transmission Class Ratings,” and Article 9.11.2.2., “Building Services in an Assembly.” Information can also be found in tables 1 and 2 of Ministry of Municipal Affairs and Housing (MMAH) Supplementary Standard SB-3, Fire and Sound Resistance of Building Assemblies, (for prescriptive selection), as well as OBC’s Article 9.32.3.9, “Fan Ratings,” the articles in Part 6 of OBC’s Section 3, and Article 5.9.1.1., “Sound Transmission Class,” and Article 5.9.1.2., “Required Protection from Noise,” in OBC.

[10]This mechanical room offers an example of the challenges of service penetrations.

Building services

Among the sources listed above, the most significant content is in OBC Article 9.11.2.2, in which the code acknowledges the fact building services in an assembly may have an adverse effect on achieving the required STC rating.

Usually, service penetrations are incorporated into various assemblies and may include, but are not limited to, the following elements:

People are typically afflicted with many sounds from building services and equipment that may affect them adversely. These can include noises from pipes, ducts, or drains, toilets flushing, high-pitched sounds, thumps or bangs, slight ticking noises, rattling at registers or grills, whistling air-conditioning, humming sounds at compressors or motors for fans or exhaust, expansion or contraction of water/air supplies, or air movement. While interior partition assemblies are usually selected prescriptively during the design phase (refer to SB-3 of OBC) and from a large number of listed assemblies lab-tested in accordance with ASTM E90, Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements, their performance in the field rarely, if ever, meets the lab results (assuming the lab tests are performed in a controlled environment with no incorporation of building services or penetrations).

In the field, interior partition assemblies are used as a component of the overall building assembly, which usually includes various penetrations and interferences of building services at a given partition as well as perimeter abutment to other building elements (e.g. window walls, curtain walls, other exterior cladding, or interior acoustically rated assemblies and partitions).

[11]Sound can navigate through the gaps at the underside of this floor/ceiling.

Risk areas

In other words, it is straightforward to maintain the STC rating of a given assembly. However, it is challenging to maintain and control the sound around transition details, construction joints, or deflection gaps where allowances have been designed to permit for structural movement and where expansion and contraction are anticipated.

Through these risk areas, the sound finds its best route to navigate the building from one suite to another and from each area to the adjacent one without any disturbances from noise control. That route may be called a weakness in the design or blind spot, or sometimes an intrusion of sounds. However, it might also be termed the path of least resistance.

A simple example would be sound propagation through the suite entrance door, where sound leaks through perimeter gaps designed as a provision for ventilation, circulation, and pressurization for odour control purposes.

In accordance with OBC, determination of actual performance in the field can be made using parameters and methods detailed in ASTM E336, Standard Test Method for Measurement of Airborne Sound Attenuation Between Rooms in Buildings. Bearing in mind field performance usually falls short of results expected based on prescriptive selections, it would be prudent to aim higher when considering prescriptive methods or paths. Additionally, paying close attention during construction is equally crucial to addressing the weak spots and ensuring the desired performance in the field (including, of course, end user satisfaction).

In most construction projects, unforeseen scenarios and site conditions force contractors, installers, and sometimes designers (if they are informed) to make some changes and modifications to the assembly that were not included in the original design. Those deviations may impact the overall performance and lead to totally unpredicted results.

Acoustical partitions should be tested in the field to ensure compliance with design intent and OBC minimum requirements. Leaving it up to the occupants to determine the practicability and performance of the acoustical wall or assembly means the consultants have not performed their duty, leaving potential gaps and complaints that could lead to litigation involving the building auditor, condo board, developer, acoustical consultant, field review consultant, and others.

[12]Mechanical units may generate a lot of noise if not designed carefully.

Comparison

Most ‘brick-and-mortar’ building construction is relatively straightforward. Live and dead load factors are evaluated and structural components and assemblies are designed to meet the calculated requirements and ensure structural integrity.

However, addressing noise mitigation is not nearly as simple as addressing structural requirements. The effects of noise are very subjective and can be more or less disruptive based on many different considerations (such as those described earlier in this article).

For example, an intermittent noise may be more disruptive than the same noise if it was constant. Some professors of neurology suggest white/pink noise can help patients sleep better. A person’s perception and ability to hear tends to vary with age, so the frequency of a given noise also plays a part. One should also consider whether the noise resonates with something in the affected space. Is one tenant’s music another’s noise?

Is the total absence of sound desirable? Probably not. Some types of noise (e.g. white noise) might be beneficial for certain individuals when trying to sleep, for example. However, there are few things more annoying than undesired noise, and the settled world is teeming with it. In fact, the air we breathe carries and surrounds us with bits of that undesirable noise. Not only does air transfer the noise, but the components of the buildings we create also provide conduits for it to transfer.

Noise seems to be quite adept at switching between these modes of transport. Materials and methods used to reduce airborne sounds are not particularly effective in combating structure-borne sound. Added to the mix is the fact with few exceptions, acoustical performance of buildings has not historically been a primary concern to builders, due to the difficulty and expense of addressing it.

The surrounding community also presents a vast array of noise generators—some constant, but most transitory (e.g. traffic). As well as community noises, a building itself provides additional noise sources, such as air movement, wind tunnel/turbulence, vehicular traffic, mechanical/electrical systems, and occupants.

While the size of the livable space may not have a critical bearing on noise control, the layout, selected material, and assemblies do.

[13]A service penetration compromising the acoustical partition.

Design and layout

Due to the many associated complications, any attempt at noise mitigation design will, at best, be a sloppy endeavour. Mitigation of various known noise sources (such as the chiller on the roof, the train passing by the block at 4:40 a.m. each day, or the subway running 24 hours a day) can be planned and have elements incorporated into the building during construction. The majority of community noise, both present and future, cannot be so easily addressed.

The best compromise for new construction (now required by most jurisdictions) consists of measuring current noise levels in the proposed building locations, extrapolating future levels, and designing the building façade to reduce the expected noise to the desired level. Individual room usage ratings will usually determine what these levels may be. For instance, the kitchen, bathroom, and hallways might have a 45-dB rating, the living room might be rated for 40 dB, and a bedroom might have a rating of 35 dB, per Canada Mortgage and Housing Corporation’s (CMHC’s) Road & Rail Noise Effects on Housing (For comparison, see an overview[14] of the noise levels various sounds produce at).

In multi-unit dwellings, in addition to requiring ambient noise levels in different areas not to exceed particular points, STC ratings are specified for construction assemblies separating uses (e.g. distinguishing a dwelling unit from the rest of the building with a minimum STC of 50 or giving a refuse chute or elevator shaft a minimum STC of 55).

In addition to these minimum STC requirements, efforts should be made during the design stage to isolate the building’s mechanical equipment as well as passive noise generators (e.g. garbage chute) from the structure, thus reducing, to some extent, the structure-borne noises. This can be achieved by using a sound control technique or underlayment, employing vibration isolation connectors, allowing provisions for clearance for duct and service penetrations, or incorporating gaskets, mounts, isolation or separation pads, resilient channel, acoustical sealant, sound-absorptive insulation, and other resilient materials to block or damp noise and vibration.

Best design and perfect execution during construction would still ultimately result in compromise, since people still need to breathe, and sound will continue to travel in air. However, analyzing potential design issues (such as the building location, orientation, and proximity to neighbouring properties and traffic, the size, volume, and shape of a given space or room, and the selection of sound-absorbing materials, isolation pads, and resilient connections) will minimize the impact of noise and vibration on the occupants and promote building durability and better performance.

It should be noted a proper noise mitigation specification, as well as a proper strategy for sound control and isolation of demising boundaries, should be co-ordinated properly between the prime consultants at the preliminary stage of design. The specification should take into consideration the size, volume, dimensions, proportions, and configuration of the rooms/interior space to eliminate echoes, reverberation, and flanking paths. This could take the form of laying out suites and adjacent rooms according to their functions. By doing so, certain awkward scenarios are eliminated, such as placing bathroom against bedroom, kitchen or living room against bedroom, bedroom against stairs, or bedroom against elevator shaft, refuse chute, gymnasium, amenities spaces, or mechanical and electrical operating systems. This approach of defining design criteria and objectives will strengthen noise mitigation and pay enormous dividends to participants and end users.

[15]Acoustical furring at demising wall in wood-frame construction.

Shop drawings and specifications

Acoustics should be reviewed from specification, design, installation, and performance perspectives. In some cases, shop drawings for the floating slab (commonly used to isolate the generator slab from the rest of the building structure) are prepared and submitted as required. In some other instances, sketches from the previous project become adopted on the new one due to building similarities and can become the only job-specific detail of this risk area or assembly. Therefore, the noise emitted by equipment may propagate to the livable space below through the lack of detailing, shop drawings, and specifications.

Equipment specs should be reviewed and carefully considered based on the project requirements. Once equipment is specified, shop drawings and detailing should follow to isolate it from the rest of the building relative to its scale, noise emission, and anticipated vibration.

Determining the type of boiler, compressor, fan coil unit, or bathroom exhaust fan in accordance with American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) recommended criteria, specifying the installation of a motor mount in an underground parking garage, or stipulating resilient connections are all critical factors for the success of any given project.

Acoustical recommendation and reporting are provided during the construction process. However, acoustical specification should also be an essential part of the process to mitigate the associated risk.

Even when one has worked on hundreds of condominium projects using specifications or project manuals to navigate through construction, one will not come across a full and comprehensive acoustical mitigation specification. Is one really needed? This question remains to be answered. However, it would make good sense to have one to complement existing specification sections by addressing job-specific requirements.

SOUND CONTROL IN CEILINGS

To combat structure-borne sound and, in particular, to enhance vertical sound isolation, soundproof ceilings are often introduced around amenity areas, exercise rooms, and mechanical/electrical equipment. This improves sound isolation and mitigates the level of discomfort caused by vibration or impact noise.

These types of acoustical ceiling assemblies could be used alone or in combination with resilient underlayment or floating slabs located at the floor above.

As is the case with any acoustical assembly, service penetrations should not be incorporated within the acoustical ceiling, as they may reduce the sound transmission class (STC) and impact insulation class (IIC) ratings and affect the overall performance of the tested assembly.

To maintain the integrity of an acoustical ceiling, piercing, penetrating, cutting, or creating openings should be prohibited, as such actions may affect the apparent sound transmission class (ASTC). Usually, tested assemblies do not incorporate service penetrations, light fixtures, hangers, or ductwork. Where these building services are required by virtue of design, a secondary drop ceiling below the acoustical ceiling is recommended as an alternative cosmetic solution to hide the building utilities and keep the acoustical ceiling intact and compatible with the desired tested assembly. In this way, building services are integrated without interfering with the acoustical design intent.

Consideration should be given to the type and method of isolation to be used at hangers, anchors, or ties meant to support the drop ceiling, ducts, or pipes. Also, it is important to control the reverberation occurring within any space—particularly within drop ceiling enclosures.

Another risk area within acoustical ceilings is the adjacent partition or boundaries and the way abutments and terminations are treated to ensure continuity of sound control and eliminate any sound leakage through the perimeters.

Conclusion

Upon close examination of acoustical aspects, it seems defining objectives and design criteria, carefully selecting construction materials and acoustically rated assemblies, choosing appropriate finishes, and diligently designing the interior space with proper layouts of adjacent areas are essential to create effective barriers to noise and vibration. This should be accomplished by taking into account Ontario Building Code standards, ASHRAE recommendations, and environmental criteria, including noise bylaws and Ministry of the Environment (MOE) guidelines.

Additionally, consideration should be given to acoustical specifications and shop drawings incorporating input from prime consultants to ensure proper implementation, addressing risk areas at abutments, transition details, and rigid connections and thereby creating more resilient assemblies to ease noise mitigation.

[16]Ibrahim El-Hajj, M.Sc., Arch., EQI, CACB, MRAIC, BCQ, OAA, is a building envelope consultant and director of building quality assurance (BQA) at McIntosh Perry. He is responsible for administering and leading the BQA department to ensure deliverables are met and to maintain compliance with the relevant construction documentation, good architectural/engineering practices, and applicable codes and standards. With more than 20 years of experience in the architectural/construction field, El-Hajj has been actively involved in a range of work pertaining to building envelope elements and cladding systems, from design and documentation review through to system failure investigation. His predominant skills include the ability to critique designs, details, and specifications and to investigate and provide accurate opinions and practical solutions. El-Hajj can be reached at i.el-hajj@mcintoshperry.com[17].